Without limiting the intended applications of the invention for all electrical systems which need improved control circuits and methods of operation and all applications generally to which the features and advantages of the invention commend it, the background of the invention is discussed in regard to a relatively specific example of controls for electronically commutated motors.
While conventional brush-commutated DC motors may have advantageous characteristics, including convenience of changing operational speeds, there may be disadvantages such as brush wear, electrical loss, noise and radio frequency interference caused by sparking between the brushes and the segmented commutator, which may limit the applicability of such brush-commutated DC motors in some fields such as the automotive and domestic appliance fields, for example. Electronically commutated motors, such as brushless DC motors and permanent magnet motors with electronic commutation, have now been developed and generally are believed to have the above discussed advantageous characteristics of the brush-commutated DC motors without many of the disadvantages thereof while also having other important advantages. These electronically commutated motors are advantageously employed, for instance, in air conditioning for cooling and warming of vehicular compartments and also in laundering apparatus. While there are some losses engendered by electronic switching of an electronically commutated motor, these are negligible compared to brush losses and rheostat losses in prior art variable speed systems.
Some circuits and electronically commutated motors are disclosed in coassigned Wright U.S. Pat. No. 4,162,435, in coassigned Boyd U.S. Pat. No. 4,528,485, in coassigned Boyd et al. U.S. Pat. Nos. 4,540,921, 4,636,936 and 4,642,536, in Alley U.S. Pat. No. 4,250,544, Alley et al. U.S. Pat. No. 4,250,435, Bitting et al. U.S. Pat. No. 4,500,821, in Young U.S. Pat. No. 4,642,537 and Archer U.S. Pat. No. 4,686,436. All of the foregoing coassigned U.S. Patents are hereby incorporated herein by reference. While the aforementioned coassigned patents, for instance, undoubtedly illustrated many features, it is believed that the control circuits for electronically commutated motors in general and for other applications could be even further improved, as well as the methods of control utilized therein.
Further improvements in control systems, electronically commutated motor systems, and methods of control and operation can beneficially contribute to more widespread use of such motors in their various applications. For example, improvements directed to increased noise immunity, fail-safe operation, economy of manufacture and greater versatility of response to various signal conditions generally would be desirable.